Recoil Speed - Zero Gravity

Two astronauts are initially floating together with zero speed in a gravity-free region of space. The mass of Major Jones is 90 kg and that of Captain Smith is 70 kg. Major Jones pushes Captain Smith away so that Captain Smith attains a speed of 0.4 m/s. The recoil speed of Major Jones is:

0.1, 0.3, 0.5, 0.7, 0.9 m/s

2. Relevant equations

P = Mv
J = change in P

3. The attempt at a solution

I honestly have no idea.. I've searched through my textbook for any similar examples of this type of elastic collision, but I can't find anything